Renewable and non-polluting sources of energy are currently in high demand. Traditional energy sources of generating energy are becoming less and less favoured due to their environmental disadvantages. It is well-known that power is available from the kinetic energy of a mass of air moving as wind and, as such, wind-powered electricity generators such as wind turbines are now increasingly becoming more attractive.
There are two basic types of wind turbines: 1) horizontal-axis wind turbines (HAWT) and 2) vertical axis wind turbines (VAWT). In HAWT the main rotor shaft and the electrical generator are typically located at the top of a tower and are pointed into the wind or parallel to the wind direction. Conversely, VAWT have the main shaft oriented vertically. One advantage of this arrangement is that the generator and gearbox can be placed at the bottom of the tower and therefore do not have to be supported at the top of the tower.
Different types of vertical axis turbines are disclosed in the prior art. For example, U.S. Pat. No. 7,083,382 discloses a vertical axis wind turbine comprising a rotating shaft to which at least one arm extends radially therefrom wherein at least one blade that is rotatably mounted to each arm. The blades are moveable from a first position having a first drag to a second position having a second drag. The first drag is higher than the second drag and thereby effects rotation of the shaft. Another embodiment is shown where multiple blades are mounted to each arm and are arranged in series so that each blade is individually rotatable.
U.S. Patent Publication No. 2007/0014658 A1 discloses a vertical axis wind mill with variable pitch flat blades and booster curtains. The variable-pitch flat blades are rotatably attached to truss-like radial arms and are rotatable about a vertical axis using a chain or belt that is driven by a motor. The booster curtains are also attached to the truss-like radial arm and can be raised and lowered using another separate motor. The movement of the flat blades and booster curtains are controlled by the weather vane.
U.S. Pat. No. 5,855,470 discloses a wind wheel having paddle plates which are rotated to face the wind in wind-direction travel and rotated edgewise when travelling against the wind. The orientation of each paddle plate is varied via the cooperation of interrelated gear trains and belt drives. The entire wind wheel is mounted to an upwind tongue that is rotatably attached to a platform and serves as a direction controller.
One known concern with vertical axis wind turbines is their comparatively low efficiency and their a rather complicated construction which may include a large number of moving parts. One reason for the lower efficiency is that the useful capture area of the blades is often low in relation to the area that is swept by the blades. Another concern is that vertical axis wind turbines have a tendency to become unstable during strong and/or turbulent winds.